Most bicycles of today are of a sit-up diamond frame design. Numerous attempts have been made to introduce recumbent bicycle designs with limited success despite their potential advantages in comfort and power production. While resistance to change has been one reason, another has been difficulty working around the geometric limitations of the recumbent design itself, to design a bicycle that is practical, stable, safe, maneuverable, and easy to ride. There have been two general classes of solutions in the more common and comfortable feet forward position. One is the long wheel base solution, characterized by Jarvis' U.S. Pat. No. 690,733 of Jan. 7, 1902. The second is the short wheel base solution characterized by Fried, (U.S. Pat. Nos. 2,482,472), Turner et.al (4,333,664), and McElfresh, 4,618,160).
Both of these general designs have been built with hand operated steering means (handlebars) below the rider's legs and above the rider's legs. While designs with steering means below the riders legs have come on the market, they have had limited market acceptance. It is the belief of the present inventor that many riders feel safer with handlebars in front of them as at least some perceived protection in the event of a crash.
An additional problem in the mass manufacture of recumbent bicycles has been that more of the basic elements of the bicycle need to be fitted to the individual rider. In diamond frame conventional bikes, the only elements that are adjustable are the seat, and to a limited extent, the handlebars. Otherwise, one frame size fits a fairly wide variety of riders. A child who starts out on a conventional 20 inch wheel bike, can graduate directly to a 26 or 27 inch wheel adult bike of present manufacture. Because of design constraints, a change of 2 or 3 inches in leg length can make a non-adjustable frame recumbent bicycle not fit its rider.
It is especially difficult to fit the short wheel base recumbents to different sized riders, and different riding conditions. The short wheelbase design is potentially much more maneuverable and easier to store than the long wheelbase configuration because of its smaller size. However its design is more complex and constrained. Its major elements (wheels, seat, steering means, and pedal power means) are constrained in their positions in order that they stay out of the way of each other and the rider while providing good rideability. Optimization of the interrelationships between these elements has never been thoroughly researched because of the difficulty in making adjustments between all elements, or each one with respect to all the rest.
In the adjustable frame semi-recumbent design of Buckler, (U.S. Pat. No. 4,925,203), the seat is adjustable with respect to the rest of the frame. However frame construction is such that seat position is taken as a variable, rather than a possible given, around which to adjust the rest of the frame.
In the present invention, the position of the seat can be set so that it just clears the rear wheel as it is moved upwardly and back, or forward and down. Its position with respect to the rear wheel can therefore be optimized according to use, and the rest of the frame adjusted to fit the rider. This makes it possible to minimize the length of the forward extension to the pedal assembly, and the total length of the bicycle, as well as to optimize geometry for rideability. While Buckler has rudimentary means to alter wheelbase and steering axis angle (by replacing parts) he does not provide any independent adjustment in pedal crank assembly position. Adjustments for rider leg length are made in the elements connecting the seat to the main frame member, moving the seat with respect to the rest of the frame. This is the only infinitely variable adjustment on the Buckler machine.
In addition the Buckler bicycle is a semi-recumbent, not a true recumbent, as is the machine described herein. As such it is not designed so that the pressure created by pushing on the pedals is directly transferred to the seat back, as is the case on a true recumbent, such as the present design. With the Buckler machine, pedal pressure is counteracted by gravity and upward tension on the steering handlebars.
The recumbent frames of McElfresh (U.S. Pat. Nos. 4,618,160), Turner et. al. (4,333,664), and Fried (2,482,472), all embody non-adjustable frame structures between the foot operated pedals and the rear wheel. Any adjustments for operator leg length on these designs compromises the position of the rider with respect to the rear wheel, a critical parameter in terms of rideability. Turner et. al. and Fried provide no adjustments other than seat position. McElfresh provides means to adjust the distance between the seat and the front wheel steering axis, but he does not provide for, or teach in his specification, adjustment of the steering axis angle. This angle in fact changes in an uncontrolled manner as the front wheel assembly is moved along the frame in his design. In addition, all of his drawings show the imaginary upward extension of the steering axis to be well ahead of the rider's body and head, a poor choice for another very important design parameter that will be discussed in greater depth later.
The prior art recumbents that most resemble the present invention are unpatented. They include the ATP, the Presto, and the Lightning. These bicycles are provided with what is termed in the industry an adjustable boom, a single telescopic member that corresponds to the front extension of the present invention. While this configuration allows the frame to be adjusted to riders of differing leg length, they suffer from two limitations. First, the single member lacks the stiffness that is inherent in the triangulated structure of the present invention. They are notorious for their flexibility, an ergonometric deficiency, as well as a possible safety hazzard. The patents of Fried and Turner, et.al. are specifically aimed at dealing with this deficiency. Secondly, prior art single adjustable boom bicycles lack the potential for vertical as well as horizontal adjustment of the foot power means.
Suspension systems for recumbent bicycle seats are more complex than those of standard bicycles, because the seat has more than one function. There has been a long tradition of providing a sprung seat on recumbent bicycles. Jarvis' original recumbent bicycle frame patent was accompanied by another (U.S. Pat. No. 690,734) for a sprung seat.
On a standard diamond frame bike, the only function of the seat is to support the weight of the rider. Any spring function is normally carried out with the use of coil springs, however flat springs also have a long tradition (see, for instance Bailey, (U.S. Pat. No. 1,502,975). On a recumbent there are two additional functions. The first is to support the back of the rider, and the second is to counteract the force of pressing on the pedals, which force is counteracted by pressure of the rider's hips against the lower seat back.
Therefore the hips must be supported from behind by means of strength equal to the toggle force produced by the straightening of the operator's legs against the pedals, which can be quite great. This force includes a well known torsional moment, caused by the fact that the pedals and the individual hips of the rider are off the centerline of the frame. This force is discussed by Fried and Turner et.al., tho they do not spring the seats on their designs.
Jarvis' seat springing solution is to have another tube parallel to the seat post, and spaced several inches behind it, reinforced by upper rear wheel stays that connect the top end of this tube to the rear fork wheel brackets. He provides rollers on the seat back that roll up and down this tube, moving with the seat bottom, whose conventional seat stem slides up and down in its conventional seat post. The seat is sprung by a coil spring inside the seat post.
McElfresh takes a different tack, designing a seat in the form of a hammock. While giving resilience, this seat forces a transfer of much of the force against the pedals to the upper back of the rider, needlessly tiring the back and torso muscles. Others such as Weaver et al have used webbed seats; however a well sprung, comfortable seat has not been designed heretofore.